The present invention relates in general to an internal combustion engine, and in particular to a method of and a device for regulating fuel-and-air mixture supplied to a combustion chamber of an internal combustion engine via a mixture-preparing device having an oxygen probe which is placed directly in the combustion chamber to deliver an output signal indicative of the actual amount of oxygen in the mixture.
In the German patent publication No. 3,028,359 a spark plug provided with an oxygen probe is described to be used in devices which control or regulate feeding of fuel to an internal combustion engine by means of immediate or so-called combustion chamber regulating process. This known spark plug is designed such that an oxygen probe is arranged in the insulator which surrounds the central spark electrode of the plug. The oxygen probe can be made of a number of materials and includes a comparison electrode, a solid electrolyte and a measuring electrode, whereby the comparison electrode and the measuring electrode are connected to a direct-current source to determine partial pressure of oxygen to be compared. Depending on whether at certain time points the partial pressure of oxygen in combustion chamber is interpreted in the sense of too rich or too lean a mixture supplied to the engine, the oxygen probe generates cyclic fluctuations of its output signal which immediately determines the condition in the combustion space.